Effect of Freezing on Ascorbic Acid (Vitamin C) Content in Selected Fruit Juices Determined by Iodimetric Titration

Abstract

This scientific study investigates the impact of the freezing process on the concentration of ascorbic acid (Vitamin C) in selected fruit juices using the iodometric titration method. The research included six varieties of fruits: guava, kiwi, orange, mango, pear, and strawberry, which were collected fresh from Misurata city markets in a suitable state of ripeness. The experimental methodology involved extracting the juice and performing an immediate chemical analysis before freezing, followed by a second analysis after three days of storage in a frozen state. The results revealed a significant variation in the initial levels of Vitamin C among the fruits. Guava recorded the highest initial concentration at 969.98 mg/L, whereas pear exhibited the lowest concentration at 27.73 mg/L. Upon analyzing the samples after the freezing period, a reduction in ascorbic acid levels was observed across all fruit juices. The degree of degradation varied significantly depending on the fruit type; orange and strawberry demonstrated the highest stability with the least percentage of loss (2.9\% and 5.9\%, respectively). In contrast, pear and mango recorded the highest loss rates, with pear losing approximately 47.6\% of its Vitamin C content. This reduction is scientifically attributed to several factors, including partial enzymatic oxidation by enzymes such as ascorbate oxidase, and structural changes in tissues caused by ice crystal formation that ruptures cell walls. Statistical analysis using ANOVA and t-tests confirmed that while freezing effectively preserves a substantial portion of the vitamin, it does not completely halt its degradation. The study concludes that the stability of Vitamin C during frozen storage is highly dependent on the specific chemical characteristics and tissue structure of each fruit.